Inhibition of the membrane repair protein annexin-A2 prevents tumor invasion and metastasis

Cancer cells are exposed to major compressive and shearing forces during invasion and metastasis, leading to extensive plasma membrane damage. To survive this mechanical stress, they need to repair membrane injury efficiently. Targeting the membrane repair machinery is thus potentially a new way to prevent invasion and metastasis. We show here that annexin-A2 (ANXA2) is required for membrane repair in invasive breast and pancreatic cancer cells. Mechanistically, we show by fluorescence and electron microscopy that cells fail to reseal shear-stress damaged membrane when ANXA2 is silenced or the protein is inhibited with neutralizing antibody. Silencing of ANXA2 has no effect on proliferation in vitro, and may even accelerate migration in wound healing assays, but reduces tumor cell dissemination in both mice and zebrafish. We expect that inhibiting membrane repair will be particularly effective in aggressive, poor prognosis tumors because they rely on the membrane repair machinery to survive membrane damage during tumor invasion and metastasis. This could be achieved either with anti-ANXA2 antibodies, which have been shown to inhibit metastasis of breast and pancreatic cancer cells, or with small molecule drugs.

Regulation of prohepcidin processing and activity by the subtilisin-like proprotein convertases Furin, PC5, PACE4 and PC7

BACKGROUND AND AIMS

Hepcidin is an iron homoeostasis regulator peptide. Loss-of-function mutations cause juvenile haemochromatosis while its over-expression results in anaemia. However, the mechanism and function of preprohepcidin conversion to mature hepcidins (25, 22 and 20 amino acid C-terminal peptides) are not well known. After removal of the signal peptide, the first proteolytic cleavage occurs within the basic motif RRRRR(59)DT, suggesting the involvement of proprotein convertase (PC) family members in this process.

METHODS AND RESULTS

Using cell transfection experiments, the processing of preprohepcidin in the human hepatocyte line Huh-7 was found to be inhibited by the Furin inhibitors serpin alpha1-antitrypsin (alpha1-PDX) and prosegment preproFurin (ppFurin). Site-directed mutagenesis analysis confirmed the RRRRR(59)DT preprohepcidin cleavage site. In parallel, the lack of preprohepcidin processing found in the PC activity-deficient cell line LoVo was restored by the expression of Furin, paired basic amino acid cleaving enzyme 4 (PACE4), PC5 or PC7. This finding is consistent with the in vitro digestions of a synthetic peptide mimicking the cleavage site of preprohepcidin. In addition, during mouse embryonic development the major expression of hepcidin found in the liver coincided with that of Furin. While hepcidin induces the degradation of the iron transporter ferroportin, its RRRRR(59) to SSSSS(59) mutant is not active.

CONCLUSIONS

These results demonstrate the key role of the convertases Furin, PACE4, PC5 and/or PC7 in the generation and secretion of active hepcidin and suggest that the control of hepcidin processing as a potential therapeutic/diagnostic strategy in hepcidin-related disorders such as haemochromatosis, inflammatory diseases, anaemia and cancer.

Mechanism of inhibition of endothelin-1-stimulated proteoglycan and collagen synthesis in rat articular chondrocytes

The aim of this study was to determine the effects of endothelin-1 (ET-1) on proteoglycan (PG) and collagen synthesis by rat articular chondrocytes (RAC). PG and collagen synthesis was measured by [(35)S]-sulphate and [(3)H]-glycine incorporation, respectively into monolayers of confluent RAC exposed to ET-1 (10(-11) M-10(-7) M). ET-1 stimulated PG and collagen synthesis in these cells in a concentration-dependent manner during the first 24 h of incubation. Prolonged contact of the cells with ET-1 resulted in a gradual decrease, and finally, inhibition of ET-1 effects. This inhibition is mediated by nitric oxide (NO) released in response to ET-1 since: (1) nitric oxide synthase inhibitor, nitro-L-arginine-methyl ester (L-NAME), enhanced both basal and ET-1-induced [(35)S]-sulphate and [(3)H]-glycine incorporations; (2) sodium nitroprusside (SNP), which spontaneously releases NO, inhibited both basal and ET-1-induced incorporations, and was also able to suppress the effects of L-NAME; (3) NO levels in the culture media were also correlated with the inhibition of [(35)S]-sulphate and [(3)H]-glycine incorporation; and (4) SNP also inhibited aggrecan and collagen II transcriptions, probably via cGMP. This effect was mimicked with 8-bromo-cGMP. Interestingly, the LY83583, which blocks the NO-dependent production and release of cGMP, inhibited PG-collagen synthesis but had no effect on their mRNA expressions. Thus, normal levels of cGMP appeared to be necessary for PG-collagen synthesis, whereas decreased levels are detrimental. In conclusion, NO, produced by rat AC in response to ET-1, counteracts the stimulation and finally induces inhibition of PG-collagen synthesis by ET-1 in these cells but NO-induced cGMP is only partially responsible for this inhibition.

Inhibition of proprotein convertases is associated with loss of growth and tumorigenicity of HT-29 human colon carcinoma cells: importance of insulin-like growth factor-1 (IGF-1) receptor processing in IGF-1-mediated functions

Proprotein convertases (PCs) of the subtilisin/kexin family are responsible for the activation of prohormones, protrophic factors, and their receptors. We sought to determine whether loss of PC-mediated activities might affect the malignant phenotypes of cancer cells. Stable transfectants of alpha(1)-antitrypsin Portland (alpha(1)-PDX) cDNA, coding for a potent PC inhibitor, were analyzed in model HT-29 cells (HT-29/PDX) and in other cell lines. Expression of alpha(1)-PDX resulted in a proinsulin-like growth factor-1 receptor (pro-IGF-1R) processing blockade, hence inhibiting the ability of exogenous IGF-1 to induce tyrosine phosphorylation of its beta-subunit and insulin-related substrate-1. Coexpression of IGF-1R with four different PCs or the novel convertase SKI-1 in the furin-defective LoVo-C5 cells demonstrated that pro-IGF-1R ( approximately 200 kDa) cleavage into IGF-1R (beta-subunit, approximately 105 kDa) can be achieved by furin and PC5A, but not by PACE4, PC7, or SKI-1. Expression of alpha(1)-PDX resulted in reduction of DNA synthesis and in anchorage-independent growth. Following serum deprivation, the alpha(1)-PDX transfectants exhibited an enhanced apoptotic phenotype and were insensitive to IGF-1-mediated [(3)H]thymidine incorporation and protection against apoptosis. These cells showed reduced invasiveness that paralleled decreased mRNA levels of urokinase-type plasminogen activator and its receptor, tissue-type plasminogen activator, and plasminogen activator inhibitor-1. Comparative subcutaneous inoculation of cells in nude mice revealed that animals injected with HT-29/PDX cells exhibited delayed and lower incidence of tumor development as well as reduced tumor size. Immunohistochemical analysis of CD31 antigen expression, a marker of endothelial cells, revealed reduced HT-29/PDX tumor vascularization. These findings indicate that PCs actively contribute to the growth and malignant phenotypes of HT-29 tumors, suggesting that PC inhibition strategies may be a useful adduct to the arsenal of colorectal anticancer gene therapies.

Developmental expression and tissue distribution of Phex protein: effect of the Hyp mutation and relationship to bone markers

Mutations in PHEX, a phosphate-regulating gene with homology to endopeptidases on the X chromosome, are responsible for X-linked hypophosphatemia (XLH). The murine Hyp homologue has the phenotypic features of XLH and harbors a large deletion in the 3' region of the Phex gene. We characterized the developmental expression and tissue distribution of Phex protein, using a monoclonal antibody against human PHEX, examined the effect of the Hyp mutation on Phex expression, and compared neprilysin (NEP), osteocalcin, and parathyroid hormone/parathyroid hormone-related protein (PTH/PTHrP) receptor gene expression in bone of normal and Hyp mice. Phex encodes a 100- to 105-kDa glycoprotein, which is present in bones and teeth of normal mice but not Hyp animals. These results were confirmed by in situ hybridization (ISH) and ribonuclease protection assay. Phex protein expression in femur and calvaria decreases with age, suggesting a correlation between Phex expression and bone formation. Immunohistochemical studies detected Phex protein in osteoblasts, osteocytes, and odontoblasts, but not in osteoblast precursors. In contrast to Phex, the abundance of NEP messenger RNA (mRNA) and protein is not significantly altered in Hyp bone. Similarly, osteocalcin and PTH/PTHrP receptor gene expression are not compromised in bone of Hyp mice. Our results are consistent with the hypothesis that loss of Phex function affects the mineralizing activity of osteoblasts rather than their differentiation.

Pex mRNA is localized in developing mouse osteoblasts and odontoblasts

Mutations in PEX, a phosphate-regulating gene with homology to endopeptidase on the X chromosome, were recently identified in patients with X-linked hypophosphatemia (XLH), an inherited disorder of phosphate homeostasis characterized by growth retardation and rachitic and osteomalacic bone disease. To understand the mechanism by which loss of PEX function elicits the mutant phenotype, a study of its mRNA localization and ontogenesis was undertaken. Using the reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) with polyA+ RNA purified from mouse testis, a 337-bp Pex cDNA fragment was generated and cloned in the pCRII plasmid. The cDNA was used to generate sense and anti-sense Pex riboprobes for in situ hybridization (ISH) and Northern analysis. To survey a large number of different tissues, sagittal sections of embryos and newborn mice were examined. ISH showed the presence of Pex mRNA in osteoblasts and odontoblasts. Pex gene expression was detectable on Day 15 of embryonic development, which coincides with the beginning of intercellular matrix deposition in bones. Finally, Northern analysis of total RNA from calvariae and teeth of 3-day-old and adult mice showed that the abundance of the 7-kb Pex transcript is decreased in adult bones and in nongrowing teeth. The present study demonstrates that Pex mRNA is expressed in bones and teeth and suggests that this putative endopeptidase plays an important role in the development of these tissues.

Basal and induced nitric oxide and cGMP productions are decreased in senescent cultured rat articular chondrocytes

The effects of interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and lipopolysaccharide (LPS) on the productions of nitric oxide (NO) and cGMP by cultured articular chondrocyte (AC) monolayers from 1-, 8- and 18-month old male Wistar rats were studied. It was found that basal NO and cGMP productions decrease with the age of animals. The productions were more than 2-fold greater in cells from 1-month old rats then in cells from older animals. IL-1, TNF-alpha, and LPS stimulated all three types of cells to produce NO and cGMP in a time- and concentration-dependent manner. Although the cells from young animals produced more NO per microg DNA, the older counterparts were more sensitive to these agents since they produced more NO upon stimulation then the corresponding non-stimulated controls. At the concentration of 10(-3) M, the nitric oxide synthase (NOS) inhibitor, Ng-monomethyl-L-arginine (L-NMA), blocked, although incompletely, both the basal and stimulated NO and cGMP productions in cells from the 1 and 8-month old rats and only induced productions in 18-month old counterparts. These results show a decreased capacity of unstimulated- and stimulated-AC from old rats to produce NO and cGMP in culture, which may affect the ageing cells in some yet unknown way.

Overexpression of ecto-5'-nucleotidase promotes P-glycoprotein expression in renal epithelial cells

P-glycoprotein (P-gp), responsible for multidrug resistance (MDR) of tumoral cells, is also expressed in apical membranes of normal epithelial cells, among which are proximal tubular cells. Ecto-5'-nucleotidase (5'Nu), co-located with P-gp in renal brush border membranes, could be instrumental in the expression of MDR phenotype. P-gp activity [assessed by rhodamine 123 (R123) and [3H]vinblastine (3H-VBL) accumulation] was evaluated in MDCK cell lines in which human 5'Nu was expressed at different levels after retroviral infection: MDCK-5'NU/- cells with a low 5'Nu activity (Vmax < 2 pmol/mg protein/min) and MDCK-5'NU/+ cells, which expressed a high level of 5'Nu (Vmax 150 +/- 18.5 pmol/mg protein/min). MDCK-5'NU/- cells did not display functional expression of MDR. In MDCK-5'NU/+ cells, R123 and 3H-VBL accumulation was significantly lower than in MDCK-5'NU/- cells and was dramatically enhanced by P-gp inhibitors. This high P-gp activity in MDCK-5'NU/+ cells was confirmed by their resistance to colchicine (measured by LDH release and MTT assay) as compared to MDCK-5'NU/- and was accounted for by increased membrane expression of P-gp assessed by Western blot. Neither AMP nor adenosine, the substrate and the product of 5'Nu, respectively, affected P-gp activity. Inhibition of 5'Nu with alpha beta-methylene-adenosine-diphosphate (alpha beta MADP) or with a blocking anti-5'Nu antibody (1E9) did not blunt MDR expression in MDCK-5'NU/+ cells. Conversely, the anti-5'Nu antibody 5F/F9, which did not block the enzymatic site, induced a decrease of P-gp activity. Further, incubation of MDCK-5'NU/- cells with conditioned medium from MDCK-5'NU/+ cells, which contained significant amounts of released 5'Nu, induced MDR phenotype.

IN CONCLUSION

(i) expression of ecto-5'Nu promotes multidrug resistance (MDR) activity in renal epithelial cells by enhancement of P-gp expression; (ii) this effect does not involve enzymatic activity of 5'Nu; (iii) supernatants of cells that express 5'Nu conferred P-gp activity to 5'Nu negative cells.

The mechanism of inhibition of DNA synthesis in articular chondrocytes from young and old rats by nitric oxide

The mechanism by which nitric oxide inhibits the incorporation of [3H]thymidine into rat articular chondrocytes (AC) in culture was studied. First-passage articular chondrocytes, isolated by collagenase digestion of cartilage fragments from humeral and femoral heads of 1- and 18-month-old rats, were used in all experiments. NO-generating compounds, isosorbide dinitrate or sodium nitoprusside, inhibited the incorporation of [3H]thymidine and the release of prostaglandin E2 (PGE2) and stimulated cyclic guanosine monophosphate (cGMP) production by rat AC monolayers in a concentration-dependent manner. The cells from old rats were much less sensitive to NO donors and also produced less PGE2 and cGMP. Blocking the production of endogenous NO with NG-monomethyl-L-arginine (L-NMA), an inhibitor of NO synthase, stimulated DNA synthesis. cGMP was found to be a key mediator of the inhibition of DNA synthesis by NO donors in rat AC. 6-Anilino-5,8-quinolinedione (LY83583), an inhibitor of NO-dependent cGMP release, stimulated [3H]-thymidine incorporation, whereas the cGMP analog, 8- bromo-cGMP, inhibited L-NMA-induced or LY83583-induced stimulation of [3H]thymidine incorporation. NO donors blocked the stimulation of DNA synthesis induced by L-NMA and only marginally blocked that of LY83583. Indomethacin had no effect on the inhibition of DNA synthesis by NO or 8-bromo-cGMP. These results show that NO donors induce inhibition of DNA synthesis probably by elevating cGMP. The relative insensitivity of senescent cells to NO donors may be due, at least in part, to their decreased capacity to produce cGMP.

Inhibition of ecto-5'-nucleotidase by nitric oxide donors. Implications in renal epithelial cells

We evaluated, in renal epithelial cells with a proximal tubule phenotype, the effect of nitric oxide (NO) on ecto-5 -nucleotidase (5'-N U), the underlying mechanism and its functional consequence. Sodium nitroprusside (SNP, 1-1000 microM), a NO donor, inhibited 5'-NU activity in a time- and concentration-dependent manner. Consequently, NO blunted the inhibition by extracellular cyclic AMP (cAMP, 10-1000 microM) of sodium-phosphate cotransport, a pathway which involves degradation of adenosine monophosphate (AMP) by 5'-NU. SNP-induced inhibition of 5'-NU was not mediated by cyclic GMP, since it was not mimicked by atrial natriuretic peptide, and was reproduced by isosorbide dinitrate and sodium nitrate, two NO donors. SNP and genuine NO decreased the activity of 5'-NU in renal homogenates, and the effect of SNP was potentiated by dithiothreitol and glutathione, but not by nicotinamide adenine dinucleotide. In vivo in rats, kidney ischemia/reperfusion, which activates inducible NO-synthase, inhibited renal 5'-NU. This inhibition was prevented by Nomega-nitro-L-arginine methyl ester, a NO-synthase inhibitor. These results indicate that: (i) NO-related activity inhibited the activity of an ecto-enzyme, 5'-NU, most likely through S-nitrosylation of the enzyme; (ii) inhibition of 5'-NU activity by NOx, which can occur in vivo under pathophysiological conditions, affected the extent to which extracellular cAMP inhibited sodium-Pi cotransport.

Parathyroid hormone stimulates ecto-5'-nucleotidase activity in renal epithelial cells: role of protein kinase-C

PTH-induced phosphaturia is exerted in part by cAMP added to the renal tubular lumen under the influence of the hormone. Modulation of renal phosphate transport by luminal cAMP requires degradation of the nucleotide into adenosine by brush-border membrane ectoenzymes, among them ecto-5'-nucleotidase (5'-NU). Hormonal modulation of 5'-NU activity was evaluated in cultured opossum kidney cells. PTH (1-100 nM) stimulated 5'-NU in a time-, concentration-, and protein synthesis-dependent manner. The effect of PTH-(1-34) was mimicked by PTH-(3-34), which does not activates adenylate cyclase, and by phorbol 12-myristate 13-acetate (PMA), but not by forskolin or (Bu)2cAMP. Down-regulation or pharmacological inhibition of protein kinase-C (PKC) abolished the effect of PTH fragments and PMA. PTH fragments increased intracellular Ca2+ and translocated PKC activity to the membrane. PTH or PMA did not affect 5'-NU messenger RNA content. Inhibition of sodium-phosphate cotransport by extracellular cAMP was decreased by 5'-NU inhibition and was magnified by PTH. These results indicate that 1) PTH stimulates 5'-NU activity in renal proximal tubular cells in a manner involving PKC activation and de novo protein synthesis; and 2) this effect participates in PTH modulation of renal phosphate transport.